1. Field of the Invention
The present invention relates to syringes and more particularly concerns a syringe suitable for prefilling including structure for preventing the contents of the syringe from exiting the needle end of the syringe barrel during storage.
2. Description of the Prior Art
Prior art hypodermic syringes include an elongated barrel having opposed proximal and distal ends and a chamber therebetween for receiving a fluid. A passageway extends through the distal end of the syringe barrel and communicates with the chamber. The distal end of the prior art syringe barrel is connected to a sharp needle cannula for delivering fluid from the chamber and passageway. The proximal end of the prior art syringe barrel slidably receives a plunger, such that movement of the plunger urges fluid through the needle cannula.
Many prior art hypodermic syringes are prefilled with fluid prior to shipment to health care facilities or other end users. Prefilling of a hypodermic syringe offers several advantages. In particular, handling of the hypodermic syringe after removal of the protective needle shield is substantially reduced. Additionally, required dosages can be carefully controlled to avoid misuse of the fluid being injected. Still further, inventory management at the health care facility can be simplified.
Contact between the prefilled fluid and the needle cannula or the passageway through the distal end of the prior art syringe barrel can cause clogging, leakage, and in some areas, possible chemical interaction between the needle and the fluid. Thus, in some cases it is desirable to isolate the prefilled fluid from the distal end of the syringe barrel and from the needle.
The prior art has included several structures for isolating the fluid in the prefilled hypodermic syringe and the distal end of the barrel. One prior art approach has included a rupturable membrane mounted at a distal location within the syringe barrel to separate the prefilled fluid from the needle and syringe tip. Slidable movement of the plunger in this prior art syringe barrel causes the prefilled fluid to increase pressure on the membrane. Sufficient pressure causes the membrane to either rupture or to deform into an inner needle which pierces the membrane. Further slidable movement of the plunger into the prior art syringe barrel causes the prefilled fluid to pass through the ruptured or pierced membrane and into the needle cannula. This prior art approach, however, creates the potential that a portion of the membrane could disengage and either block the needle cannula or pass entirely therethrough.
Other prior art prefilled hypodermic syringes have included a syringe barrel with an enlarged cross section near the distal end. A stopper is slidably disposed in the syringe barrel proximally of the enlarged cross-section to isolate the prefilled fluid from both the needle and the enlarged cross-sectional region of the barrel. Slidable movement of the plunger into this prior art syringe barrel moves the stopper distally and into the region of enlarged cross-section. The fluid then bypasses the stopper and flows into the needle cannula. The non-uniform cross-section along the length of this prior art syringe barrel can complicate manufacturing processes and increase manufacturing costs.
Still other prior art syringes have included isolation stoppers which deform, when they reach the distal end of the barrel, in response to the increased pressure of the fluid generated by the slidable movement of the plunger. Prior art devices of this type may require uncertain or excessive pressure on the plunger and require a higher pressure throughout the injection process because they close the fluid path to the needle when the pressure is reduced.